1. Field of the Invention
The present invention relates to a method of manufacturing a cushioning member such as a sun visor. More particularly, it relates to a method of wrapping a cushioning member in a web of wrapping material formed from two blanks. One blank is placed on one main surface of the cushioning member and the second blank is placed on its other main surface, each blank forming a peripherally protruding flange at the center plane of the cushioning member. The flanges are clamped between two web electrodes which face each other and are welded peripherally to each other by high-frequency welding so as to form an inwardly directed weld bead by the flow of material at the flange edges facing the member. The invention also relates to an apparatus for carrying out this method.
2. Description of Related Art
In the manufacture of equipment parts of automotive vehicles which serve as a cushioning members, such as head rests, arm rests, and sun visors, as well as similar articles outside the automotive industry, PVC foils which are connected to each other by high-frequency welding are frequently used as wrapping material. High-frequency welding of plastic material is obtained by the dielectric heating of nonconductive polar substances in a high-frequency electrical field. This is a reliable and rapid method which has the further advantage that the weld excess can be torn off, without the use of a special tool, along a residual film directly after the welding. Thus, a clean, smooth weld seam remains which requires little or not additional working.
However, this is not possible when the dielectric weld material consists in part of fabric, leather or the like which is to be included in the weld or anchored in the thermoplastic foil.
There are several reasons for this problem. First of all, ordinary flat textile structures, as well as leather or other non-plastic materials, cannot be welded with high frequency and must therefore be coated with a material that can be welded by high frequency, so as to make such materials attachable to a base or to each other. More serious, however, is the problem that it is not possible to tear off the weld residue when using these materials. In the case of a coated textile material, for instance, the fibrous material is not softened by the high-frequency welding, and thus cannot easily be torn. Such coated textile material (as well as leather or the like) therefore must be cut around the weld seam or be removed from the weld residue by stamping. Three methods for this have become known (see HF SCHWEISS-TECHNIK, G. F. ABELE, ZECHNER & HUTHIG VERLAG, SPEYER, 1965 pages 269-275).
In the first method, the stamping tool also serves as the welding electrode. This tool is first of all brought, together with the material, to the welding press and then to the die.
In the second method, in order to obtain a strong weld connection, the welding tool and the stamping tool are functionally or even spatially separate. In forming such a connection, assuming such spatial separation, a web weld is first effected on a standard welding press and the welded material is removed from the electrode or press and fed to a stamping tool.
The necessity of repeated insertion operations in these first and second methods led to the desire to rationalize and simplify this manufacturing field. A further desire was to eliminate uncertainty as to whether the stamping was being effected with proper register. The result was a third method, in which a combined welding-stamping tool is brought, charged with material, to welding and stamping presses in succession. The welding and stamping presses may be arranged, in actual practice, around a rotary table.
In these known methods, which appear without exception to be rather expensive, a weld rim of excess weld material always remains, which constitutes a disadvantage. Another particular disadvantage resides in the fact that the stamping knives must always cooperate with a stamping plate. In view of the fact that a non-thermoplastic semi-finished product (leather, flat textile structure, or the like) can be cut only with a high stamping pressure, it is necessary to use particularly hard steel tools which stamp against an even harder steel bottom plate.
In general, the trend can be noted in the automobile industry toward manufacturing equipment parts of the aforementioned types so as to have a uniform appearance. If a ceiling covering, for instance, consists of a textile material, as is increasingly the case, then the sun visor should also be wrapped with this same textile material. Yet, it has been inconvenient to manufacture such uniform parts in the past, for the reasons already mentioned.